fix(image): stop darkening rasters; X only for broken references

Image textures were created Rgba8UnormSrgb: sampling decoded sRGB to
linear, but the surface isn't sRGB, so every raster (images, OLE, PDF
underlays) rendered visibly dark. Rgba8Unorm passes the texels through
in the same space as every other colour in the app.

The frame wire also always carried the X diagonals — that's the
broken-reference placeholder, and it scribbled over resolvable images.
The diagonals now draw only when the reference doesn't resolve.

Co-Authored-By: Claude Fable 5 <[email protected]>

src/entities/raster_image.rs

@@ -93,6 +93,11 @@ impl TruckConvertible for RasterImage {
         // place the boundary where AutoCAD draws it. Must match the raster's
         // own clip triangulation in `ImageModel` so outline and pixels align.
         let ih = self.size.y;
+        // Diagonals are the BROKEN-reference placeholder; a resolvable image
+        // draws its pixels inside the frame, so the X would scribble over it.
+        let path_probe = self.file_path.trim();
+        let resolvable = path_probe.is_empty()
+            || crate::scene::model::image_model::resolve_image(path_probe).is_some();
         let pts = if self.clipping_enabled {
             let cb = &self.clip_boundary;
             match cb.clip_type {
@@ -116,10 +121,10 @@ impl TruckConvertible for RasterImage {
                     let c3 = px_to_world(xa, yb);
                     vec![c0, c1, c2, c3, c0]
                 }
-                _ => image_wire(corners, true),
+                _ => image_wire(corners, !resolvable),
             }
         } else {
-            image_wire(corners, true)
+            image_wire(corners, !resolvable)
         };
 
         // A raster OCS can display renders its pixels (built separately) inside

src/scene/pipeline/image_gpu.rs

@@ -94,7 +94,7 @@ impl ImageGpu {
             mip_level_count: 1,
             sample_count: 1,
             dimension: wgpu::TextureDimension::D2,
-            format: wgpu::TextureFormat::Rgba8UnormSrgb,
+            format: wgpu::TextureFormat::Rgba8Unorm,
             usage: wgpu::TextureUsages::TEXTURE_BINDING | wgpu::TextureUsages::COPY_DST,
             view_formats: &[],
         });